Audiology and hearing-test interpretation — formative SAQs

SAQ 1 (10 marks)

A 5-week-old infant is referred to the clinic after a referred newborn hearing screen on the right ear. The diagnostic testing shows robustly present otoacoustic emissions at all frequencies on both ears, but the auditory brainstem response on the right shows no reproducible wave V even at high stimulus levels, with a preserved cochlear microphonic. ^{[11] [1]}

1. State the most likely diagnosis and the audiological findings that support it. (3) ^[11]
2. Explain why an otoacoustic-emissions-only newborn screen would have failed to detect this condition. (3) ^{[11] [2]}
3. Outline the management of this child, including the role of amplification and the team involved. (4) ^{[11] [1]}

Model answer — SAQ 1

(1) Diagnosis and supporting findings (3). The most likely diagnosis is auditory neuropathy spectrum disorder (ANSD). The supporting findings are the dissociation between the otoacoustic emissions and the auditory brainstem response: the OAE are robustly present, confirming that the cochlear outer hair cells are functioning; the ABR on the right is absent with no reproducible wave V even at high stimulus levels, confirming that the auditory nerve or its synapse is not conducting a synchronous response; and the cochlear microphonic is preserved, which rules out a severe outer hair cell (cochlear) loss and localises the failure to the neural-synaptic part of the pathway. This pattern is the signature of ANSD and is seen, for example, in OTOF-related hearing impairment. ^[11]

(2) Why OAE-only screening fails (3). Otoacoustic emissions report only on the cochlear outer hair cells — the biological amplifier at the sensory end of the pathway. In ANSD the outer hair cells are intact, so the OAE are preserved and an OAE-only screen reports a pass, while the neural pathway that actually carries the signal to the brain is impaired. The ABR is the only screening modality that interrogates the whole pathway from cochlea to brainstem, so a two-stage protocol that includes automated ABR (aABR) is required to detect ANSD. This is the structural limitation of OAE-only screening and the reason most modern programmes use a two-stage OAE then aABR protocol. ^{[11] [2]}

(3) Management (4). The child is managed by a multidisciplinary team led by paediatric audiology and ENT, with the family enrolled in early intervention services. The management diverges from a typical sensorineural loss because amplification may improve detection without restoring the intelligibility of speech — the hallmark difficulty of ANSD is that sound is heard but not encoded for timing. The team weighs hearing aids calibrated to the ABR thresholds, FM or remote-microphone systems to improve the signal-to-noise ratio, and, where speech perception remains poor despite a trial of amplification, cochlear implantation, which can be highly effective when the lesion is at the synapse (as in OTOF-related ANSD). The child needs ongoing behavioural and electrophysiological monitoring, and the family needs honest counselling that the trajectory and the benefit from each intervention are individualised and audiology-led rather than protocol-driven. ^{[11] [1]}